In previous research, pigeons entered one situation with two or more keys available on which pecks produced food or a second with only a single key available. These two situations, the terminal links of concurrent-chain schedules, can be treated respectively as conditions of free choice and of forced choice. Pigeons preferred free choice to forced choice; technically, in the concurrent initial links of the schedules, pigeons maintained higher response rates in producing free choice than in producing forced choice, even with the situations equated in terms of time per reinforcer, responses per reinforcer, and relative frequency of exposure. Later experiments explored properties of terminal-link stimuli, number of free-choice alternatives, and the pigeon's previous history with choices. The free-choice preference has not been reducible to simpler variables, such as number of conditioned reinforcers or propeties of terminal-link performances. The proposed research will examine a methodological innovation, in which pigeons will initiate contact with experimental conditions throughout extended daily sessions. This will allow behavior to be studied with minimal deprivation and more effective use of laboratory resources. Aspects of the free-choice preference to be studied will include temporal parameters of the schedules, details of terminal-link performances, and the relation between number of free-choice keys and key area (data so far suggest a number of keys is important but key area is not). Preference for free choice of different reinforcer (e.g., food and water) also will be explored, extending an earlier but limited demonstration. Two further concerns will be whether the preference has phylogenic or ontogenic origins and with its implicatons for defining behavioral units. The relation of the findings to analogous human preferences may be of both theoretical and practical interest; the availability of choice has been implicated in outcomes for human behavior in a variety of mental-health settings.